Rhizobitoxin

The key step in the total synthesis of rhizobitoxine is the Pd-catalyzed exchange reaction of the methyl alkenyl ether moiety in 4 with the functionalized alcohol, although the yield is low[3]. The enol pyruvate 6 (a-ethoxyacrylic acid) is prepared by the reaction of methyl a-methoxyacrylate or a-methoxy-acrylic acid (5) with ethanol catalyzed by PdCl2(PhCN)2 at room temperature in the presence of CuCli and NaH2P04[4],... 

Rhizobacteria, deleterious, 13 349 Rhizobitoxine, 13 300 Rhizobium-legume associations, in nitrogen fixation, 17 296-298 Rhizofiltration, 3 783-784 defined, 3 759t Rhizopus nigricans, 11 4, 9 Rhizosphere defined, 3 1 bit RHO A-alumina, 2 394-395 Rhodacarborane catalysts, 4 217-218 Rhodamine B... 

There are only a few instances in which amino acids have been implicated in allelopathy and in most cases the specific amino acids have not been identified. Rhizobitoxine is produced by certain strains of Rhizobium japonicum and is a nonprotein amino acid (84). Several of the phytotoxins produced by pathogenic microorganisms are polypeptides and related glycopeptides (82). 

A phytotoxin from the nodules produced by Rhizobium japonicum on the roots of soybean (Glycine max (L.) Merr.), termed rhizobitoxine, was identified by Owens et al. (231, 232, 233) as 2-amino.4-(2-amino-3-hydroxypropyl)-trans-but-3-enoic acid. Another closely related analog of rhizobitoxine,... 

Production and Inhibition of Ethylene. Now I would like to illustrate how knowledge about a plant hormone can be used to control and regulate its action. Methionine is the precursor of ethylene in plant tissues (30). Therefore, any compound which blocks methionine metabolism might be expected to inhibit ethylene biosynthesis. Rhizobitoxine was recognized as an inhibitor of methionine biosynthesis (31) as were its analogues shown in Figure 6 (32). 9... 

L-2-amino-4-(2-amino-3-hydroxypropoxy)-trans>-3-butenoic acid (Rhizobitoxine)... 

These enol ether-substituted amino acids are natural products isolated from the fermentation broths of Rhizobium japonicum (rhizobitoxine) (31), Pseudomonas aeruginosa (methoxy analogue) (33) and a species of Streptomvces (ethoxy analogue) (34). 

Rhizobitoxine. Various Rhizoblum. laponlcum strains produce rhizobitoxine [75], whose structure was reported In 1972 (2691. Although the host of this bacterium Is soybean, this compound Is also phytotoxic to many other plant species. This phytotoxin Is an analog of cystathionine and acts as an Irreversible Inhibitor of -cystathlonase which catalyzes production of homoserlne from cystathionine (2701. Rhizobitoxine also Inhibits ethylene production from methionine (2711. as does a similar phytotoxin, 2-am1no-4-methoxy-3-eno1c acid (28). 

Pd(OAc)2 coordinated with 1,10-phenanthroline or 2,2 -bipyridine is a highly reactive catalyst for the exchange reaction of vinyl ethers. As shown in Scheme 56, only vinyl ethers are formed, the formation of acetals being completely suppressed77. Smooth exchange reaction under mild conditions has been applied to the total synthesis of rhizobitoxine (185). The key step is the palladium-catalyzed exchange reaction of the vinyl ether moiety78. ... 

C7H,4Nj04, Mr 190.20, hygroscopic cryst., mp. 175-179°C, [a]o +78.9° (HjO). R. is responsible for chlorosis in plants that have been attacked by Rhizo-bium japonicum and Pseudomonas andropogonis. R. irreversibly inhibits )8-cystathionase in bacteria and plants and thus prevents the conversion of methio-nine to ethylene in the plants. The biosynthesis proceeds from aspartic acid via homoserine and 4-hy-droxythreonine to rhizobitoxin. 

Rhizobitoxine, a compound similar in structure (Owens et al., 1972) to cystathionine,... 

Rhizobitoxine HOCHiCH(NHj)CHjOCH==CHCH(NHj)COOH Cystathionine HOOCCH(NHj)CH2SCHjCHjCH(NHj)COOH... 

Thus, cell enlargement, for instance, depends upon auxin and involves the uptake of water, extension of the cell membrane and protein synthesis. The auxin dose-response curve consists of two peirts promotion by low concentrations and inhibition by higher concentrations via the formation of ethylene. Cytokinins and abscisic acid may possibly induce also, under special conditions, the production of ethylene. Many publications deal with effects of these plant hormones, especially of auxin, on ethylene biosynthesis in plants which occurs after a lag phase of 30 - 60 minutes and is specifically blocked by rhizobitoxin as well as by inhibitors of ENA and protein synthesis indicating that a continuous synthesis of protein is required for high rate of ethylene production (Eef. 20). 

A similar peptide toxin, rhizobitoxin (16), is produced by the root-nodulating organism Rhizobium japonicum. Rhizobitoxin causes chlorosis in the developing leaflets of plants, such as soybean Glycine max), which have nodules colonized with these strains of Rhizobium japonicum (Mitchell, 1981). This compound is a irreversible inhibitor of ethylene production from methionine, as it blocks the conversion... 

Many naturally occurring irreversible enzyme inhibitors also exist. These are referred to as toxins. A well-known and intriguing toxin is the / ,y-unsaturated amino acid rhizobitoxine, produced by Rhizobium japonicum. This natural metabolite is a highly specific irreversible inhibitor of pyridoxal-hnked jS-cystathionase from bacteria and plants (318). 

Exchange Reactions of Vinyl Ethers and Esters. Vinyl ethers are activated by Pd. Exchange with other alcohols to give mixtures of acetals and vinyl ethers is catalyzed by PdC (eq 41). This reaction was used as the key step in the total synthesis of rhizobitoxine (eq 42). ... 

Rhizobitoxine, an analogue of cystathionine produced by certain strains of Rhizobium japonicum (Owens et al., 1972), is a potent irreversible inhibitor of plant cystathionine 8-lyase both in vivo (Giovanelli et al., 1973) and in vitro. Inhibition of the purified spinach enzyme was of the active-site-directed irreversible type (Giovanelli et al., 1971), and probably involves covalent linkage of a cleavage product of rhizobitoxine to the pyridoxal phosphate prosthetic group of the enzyme. 

Giovanelli, J., Owens, L. D., and Mudd, S. H., 1971, Mechanism of inhibition of spinach 3 cystathionase by rhizobitoxine, Biochim. Biophys. Acta, 227 671. 

Structure of rhizobitoxine, an antimetabolite enol-ether amino acid from Rhizobium japonicum, J. Chem. Soc. Chem. 

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